Method and apparatus for automatically detecting defects and irregularities in glass sheet

ABSTRACT

Method for automatically detecting defects and irregularities contained in or on the surface of glass sheet. The method includes scanning laser beams on the glass sheet and with a laser detector, detecting the presence of defects by measuring the decrease of light input reaching the laser detector as a result of dispersion of the laser beam by the defects. Apparatus for carrying out method.

Unite States Patent 1191 Nagae [4 1 June 5, 1973 [54] METHOD ANDAPPARATUS FOR 3,510,664 5/1970 Nichols ..345 209 X 3,524,988 8/1970Gaither ..250/219 DF AUTOMATICALLY DETECTING 3,612,702 10/1971 Troll..250/219 DF X DEFECTS AND IRREGULARITIES IN 3,188,478 6/1965 Binks..250/219 DF GLASS SHEET 2,993,402 7/1961 Dunipale et a1. .250/219 TH xInventor: Yasuyuki g Sakabshi Osaka, 3,174,046 3/1965 Lindemann et a1..250/219 DF Japan Primary Examiner-Walter Stolwein [73] Assignee:Central Glass Company, Limited, Attorney-Joseph M. Lane, Richard L.Aitken,

Yamaguchi-ken, Japan Donald R. Dunner [22] Fi1ed: Oct. 20, 1971 21App1.No.: 191,030 [57] ABSTRACT Method for automatically detectingdefects and irregularities contained in or on the surface of glass"250/219 258 1 sheet. The method includes scanning laser beams on 58]Field 219 Th the glass sheet and with a laser detector, detecting the250/222 203 I61 presence of defects by measuring the decrease of lightinput reaching the laser detector as a result of dispersion of the laserbeam by the defects. Apparatus for [56] References Cited y g out methocLUNITED STATES PATENTS 3,199,401 8/1965 Sleighter et al ..250/219 DF X 22Claims, 7 Drawing Figures I 5 W I 1 l 6 I, 10 o '14 METHOD AND APPARATUSFOR AUTOMATICALLY DETECTING DEFECTS AND IRREGULARITIES IN GLASS SHEETBACKGROUND OF THE INVENTION The field of this invention relates to amethod and apparatus for automatically detecting defects andirregularities contained in sheet glass, such as small pieces ofundissolved solids, ceramic materials, bubbles, surface scores andscratches.

Defects and irregularities contained within or on the surface of sheetglass deteriorate the quality of the sheet glass. Such defects andirregularities give rise to many problems in the manufacture of sheetglass. For example, in some instances, the sheet glass is manufacturedby molding molten glass in a glass melting furnace and is removed fromthe furnace with the molten glass containing impurities. Theseimpurities result from the starting materials of the glass or fromundissolved pieces of bricks or ceramics which are eroded from thefurnace walls during melting. When the sheet glass is taken up and heldbetween take-up rolls, the presecne of such defects and irregularitiesproduces cracks or fissures in the surface of the sheet glass, whichrapidly grow larger due to the heat distortion to which the sheet glassis subjected. As a result, the sheet glass may crack and shatter duringthe transfer operation.

A method which has been utilized to overcome this problem is to visuallyexamine the sheet glass before the glass reaches the first take-uprollsfor defects or irregularities and allow the rolls to widen andrelease the glass so as to pass over the defects and irregularities asthey are noticed. This method, however, requires continuous and completesupervision of sheet surface throughout the entire surface thereof inorder to detect the defects and irregularities, which in some cases areas small as 0.5 mm to 1.0 mm. Such inspection is extremely tedious andsusceptible to error.

To automatically detect the defects contained in transparent sheetglass, a method has been used which includes irradiating ordinary lightbeams on the sheet glass to detect the presence of defects andirregularities by measuring the weakening influence of such defects orirregularities on the light beam. However, ordinary light rays cannot begenerated in a narrow beam and beams which obliquely enter the sheetglass tend to expand or disperse when passing through the sheet glass orare reflected by the glass sheet. Therefore, the detection of smalldefects with ordinary light is difficult.

SUMMARY OF THE INVENTION The detection apparatus of the presentinvention includes a laser generator for generating laser beamsforautomatically detecting defects, such as small pieces of broken brick orceramics, bubbles and surface cracks contained in the sheet glass.

The method of operation includes scanning these laser beams over thesurface of glass. Since a narrow and parallel or collimated beam ofsingle wavelength light energy is obtained from a laser generator, itsuse will provide beams which will not expand when encountering varyingindexes of refraction as they pass across the sheet glass, enablingdetection of extremely fine defects and irregularities. Since there isno spreading of the beam even when passing through glass with varyingindices of refraction, beams oblique to the glass sheet can detect smalldefects. Furthermore, since the laser generator produces narrow,collimated light of high intensity, the apparatus can be made small insize relative to the ordinary light type apparatus.

Accordingly, it is an object of the present invention to provide amethod for automatically detecting the defects and irregularitiescontained in or on the surface of sheet without visual inspection.

Another object of the invention is to provide a method for automaticallydetecting the defects and irregularities contained in or on the surfaceof sheet glass which can detect defects and irregularities smallerthanthose capable of visual detection.

Still another objectof the invention is to provide a method ofautomatically detecting defects contained in sheet glass throughout thewidth of a large glass sheet.

A further object of the invention is to provide a method ofautomatically detecting defects in sheet glass and indicating thetransverse location of the defects in the longitudinal sheet glass.

Another object of the invention is to provide a novel apparatus fordetecting defects in sheet glass.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway frontelevation view of an apparatus for the manufacture of sheet glassincluding the detection apparatus of the present invention;

FIG. 2 is a cross-sectional view taken along line X-X of FIG. 1;

FIG. 3 is a perspective view of the detection apparatus of the presentinvention;

FIG. 4 is a diagrammatic view illustrating the operation of theapparatus of FIG. 3;

FIG. 5 is a block diagram schematically showing a detection circuit ofthe invention;

FIG. 6 is a diagrammatic representation showing the waveforms of anoutput voltage for a laser detector used in the detection system; and

FIG. 7 is a diagrammatic view showing an alternate embodiment of thedetection apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show an apparatusfor manufacturing sheet glass utilizing the vertical take-up systemwhere molten glass material 1 is introduced into the system from amelting furnace into a pit 2. Over pit 2 is a drawing tower 3 providedwith a number of paired take-up rolls 4. Between paired rolls 4 a moldedglass sheet 5 advances upwardly as it is taken up from the pit 2 afterpassing through a drawing block 6 and cooler 7. With this type of systemthe molten glass 1 is subject to containing a high level of impurities.Fissures or cracks are produced at locations in sheet 5 where theseimpurities are present when the sheet glass passes between the rolls 4.-

In accordance with the present invention, to detect these impurities,drawing tower 3. is provided with a defect detection apparatus. Thedetection apparatus comprises a laser light generator 10 and a laserdetector 20. Generator 10 and detector 20 are v positioned below thefirst paired take-up rolls 4 and are positioned with respect to glasssheet 5 so that laser beams pass through the glass sheet 5. To enablethe laser beam to pass through tower 3 and reach detector 20, tower 3 isprovided with windows W1, W2 (FIG. 3).

'As shown in FIGS. 3 and 4, the laser generator 10 is arranged at oneside 5' of the glass sheet 5. The generator consists of a laseroscillator 11, a group of converging lenses 12 and a polyhedral rotarymirror 14ro-' tatable at a fixed speed by a motor 13. The components ofgenerator 10 are contained within a housing 15. The laser oscillatorswhich may be utilized in practicing the invention are gas lasers, liquidlasers, crystal lasers, glass lasers and semi-conductor lasers. In thepreferred embodiment of the invention, laser oscillator 11 is a He-Negas laser oscillator which generates laser energy at a wavelength of6328 A.

The relation of the polyhedral rotary mirror 14 to laser beam 16 isshown in FIG. 4. The diameter of beam 16 is extremely narrow, forinstance, approximately 1 to 2 mm. When the laser beam strikes onemirror face of the polyhedral rotary mirror 14 while rotating in thedirection of arrow, it is initially reflected in the direction of arrowL,. As the mirror rotates, laser beam 16 is reflected through the glasssheet 5, until the reflected beam reaches a position indicated by arrowL Thereafter the beam 16 strikes the next mirror face on the polyhedralrotary mirror 14, which enables repetition of the scanning patterntoward position L from position L Thus, the rotation of the polyhedralrotary mirror 14 causes beam 16 to repeatedly scan over the glass sheet5 from an oblique direction.

The laser detector 20 includes a light converger 21, a photoelectricconverter 22 for generating an electric signal in response to the amountof incident light, and a housing 23 for the converger and converter. Inthe preferred embodiment, the light converger 21' is a flexible bundleof glass optical fibers (commonly referred to in the art as flexiblefiber optics). The end surface of the fiber optics is in a rectangularshape and forms a light receiving surface for the laser beam 16. Theother end surface of the fiber optics bundle is in a circular shape andcontacts a light receiving window in the photoelectric converter.

Output of the converter 22, which in the preferred embodiment is aphotoelectron multiplier, is supplied to a detection circuit 30. Theoperation of detection circuit 30 is described below.

The method of detection according to the present invention isillustrated with reference to FIG. 4 where the laser beam 16 repeatedlyand unidirectionally moves between positions L, and L in the mannerdescribed above, with the portion of beam 16 which covers the entiresurface of sheet glass 5 falling upon the laser light detector 20. Ifdefects or irregularities are not present in the glass sheet 5, a majorportion of the energy in the beams 16 will strike thelaser lightdetector 20, while a minor portion of theenergy in the beams will bereflected from the surface of the sheet glass or will be attenuatedduring their passage through the interior of the sheet glass.Accordingly, a voltage or other electrical signal of a magnitudeindicative of the amount of incident lightisobtained from the laserlightdetector 20. However, defects or irregularities are present in the glasssheet 5, such defects will disperse the beams 16, or absorb and obstructthe passage of the beams, so that the expected amount of light incidenton. the detector 20 suddenly decreases. As aresult, the electric signaloutput of detector 20 will decrease abruptly in response to the decreaseof the incident light. Variations of this output are analyzed todetermine the presence orabsence of defects and irregularities.

One embodiment of the detection circuit 30 is shown in FIG. 5. Theoutput of the photoelectric converter 22 is amplified by a pre-amplifier31 and then passed to a peak value discriminator circuit 32, frequentlyreferred to in the art as a threshold detector. A variable resistor 35connected to circuit 32 establishes a predetermined voltage level withwhich the output of the pre-amplifier 31 is compared. When the output ofthe pre-amplifier 31 decreases below the predetermined voltage level, apulse appears at the output of the discriminator 32. The output of thediscriminator 32 is sampled during each scan period by means of atwo-input AND gate (not shown), or the logic equivalent thereto. Oneinput to the AND gate is in the output of the discriminator 32 while theother input to the AND gate is connected to a reference signal source(not shown) synchronized with the scanning of beam 16 by rotary mirror14 (FIG. 4). The AND gate thus inhibits or blocks the output of thediscriminator 32 between scans of the glass sheet 16. Pulses whichappear at the output of the AND gate are amplified by a pulse amplifiercircuit 33 and then passed to an output control circuit 34. For example,the output control circuit 34 may include a monostable circuit whichoutputs an alarm or control signal, termed a defect signal, for apredetermined period of time to alert the operator to the presence ofdefects or irregularities in the glass sheet 5.

Waveforms of the output of the laser detector 20 are shown in FIG. 6. Inthe diagram, the abscissa indicates time t and the ordinate the outputvoltage v of the photoelectric converter 22. The output voltage isapproximately rectangular if defects or irregularities are not present.In the absence of defects, the output voltage is continuously highduring the scan period T. In the time interval between successive scansthe output of the converter 22 is continuously low. During the scanperiods, if defects are present, the output reduces abruptly when thebeam 16 strikes the defective area, producing negative going voltagespikes as shown at 24 and 25. By detecting these rapid decreases ofoutput voltage during a scan period, it is possible to discriminatebetween the presence and absence of defects or irregularities in theglass sheet 5. The magnitude of the voltage variation at 24 or 25, forexample, is proportional to the dimensions of the defects orirregularities. Dashed line 26 of FIG. 6 represents the discriminatorvoltage level predetermined by setting the variable resistor 35 (FIG.5). By changing the set value of the variable resistor 35 and therebyadjusting the predetermined level 26, it is possible to achieve optimumsensitivity of the detection circuit 30 with respect to the dimensionsof the defects to be detected. Thus, for example, if the predeterminedlevel 26 is determined as shown in FIG. 6, the defect represented byspike 24 will not be detected, but the defect at 25 will be detected.Thus, during the second scan period, as shown in FIG. 6, thediscriminator 32 would produce an output pulse which would be gatedthorugh the AND gate and amplified in pulse amplifier 33 to trigger theoutput control circuit 34.

In the embodiment described above, the amount of light incident on thelight converger 21 is represented as pne blocker unit per scan periodand the variation within the whole unit is detected; that is to say, asingle pluse is obtained for one scan period and defects are detected bythe variation from the peak or normal high value of the pulse voltage.If the light converger 21 is divided by optical construction into acellular form (not shown), during one scan period a sequence of 5 pulsescan be obtained corresponding to the divisions or cells in the lightreceiving end of the converger 21. Accordingly, it is possible to detectthe position and dimensions of defects by nothing in which cell aparticular voltage variation occurred. Alternatively, the converger 21may be replaced by an array of photoelectric converters 22 (not shown)arranged such that the beams 16 consecutively enter the converters. Theposition of defects is similarly determined when using the describedalternative method.

To insure that all of the surface of the glass sheet 5 is scannedwithout exception, the relationship between the take-up speed of theglass sheet 5, the rotational speed of the mirror 14 and the number ofmirror faces on the mirror 14 may be determined so as to satisfy thefollowing formula:

n-N thus .b

where n represents the number of faces on the rotary mirror 14, Nrepresents the rpm. of the mirror motor 13, b represents the diameter(mm) of beam 16, and a represents the take-up speed (mm per minute) ofthe glass sheet 5.

It is also possible to determine the location of the defects by usingthe defect signal issued from the detection circuit 30. This can beaccomplished by noting the relation of the time t (FIG. 6) of the defectsignal relative to the scan period T. For example, if the defect signaloccurred half-way through the scan period T, the

defect would be known to be located in the middle of the glass sheet onthe path through which the beam 16 had just been swept.

To produce the scanning of the laser beam, the rotary mirror 14 may bereplaced by a single mirror oscillating back and forth at apredetermined constant' frequency.

The embodiment as hereinbefore described shows an example in which theinvention is applied to apparatus for manufacturing sheet glassaccording to the vertical take-up system. The invention, however, is notconfined to this case but is applicable likewise to apparatus formanufacturing sheet glass in which the glass is taken out in thehorizontal direction, or similarly to apparatus in which the sheet glassproduct is inspected while it is transferred to another location, by asystem allowing the detection of defects and irregularities continuouslyas in the preceding cases. It will be noted that the present inventioncan be utilized for the detection of bubbles, surface scars and cuts inaddition to the above mentioned defects and irregularities such aspebbles and brick pieces. To sum up, the invention can be extensivelyutilized to detect the presence in glass of anything which may affectthe amount of light incident on the light receiving means.

It is, of course, possible to detect defects and irregularities presentonly on the surface of the sheet glass by using the light which isreflected from the glass rather than the light transmitted therethrough.This is accomplished by relocating the light receiving means such thatonly laser light reflected from the surface is received. FIG. 7 is anexample showing the above mentioned case. The laser beam 16 produced bythe laser oscillator 11 is reflected by the oscillating or vibratingmirror 17, and the reflected light is split into two directions by asemi-reflective mirror or beam splitter 19. The light is projected inone direction onto one side of the glass sheet 5 by a fixed mirror 18.The light from mirror 18 is reflected from the surface of the glasssheet and enters a light converging means 21, or a light converginglens, oriented obliquely with respect to the plane of the sheet 5. Thelight beams which are passed in the other direction by the beam splitter19 are projected onto the other side of the glass sheet 5 by a pair offixed mirrors 18 and 18". The light beams from mirror 18" reflected fromthe glass sheet 5 are received by I another light converging lens 21,oriented similarly to lens 21. The optical light transmitting axes ofmirror 18 and mirror pair 18', 18" are oriented so that lighttransmitted through the glass sheet from either side will not fall oneither lens 21 or 21'. The light beams reflected from the opposite sidesof sheet 5 pass through light filters 24 and 24' and are converted intoelectric signals by the photoelectric multipliers 22 and 22 respectively. The output of each multiplier is passed to a respectivedetection circuit 31 or 31, each of which may comprise the samecomponents as shown in FIG. 5 for circuit 30. The aforementioned lightreceiving means may preferably use fiber optics as described above as analternative for the converging lens system. In such case, the lightconverging means consisting of glass optical fibers has the advantage ofsimpler adaptation to the light receiving means since the end of thefiber optical element can assume the desired shape of the lightreceiving surface and lead the light to a light receiving window of thephotoelectric converter, thus avoiding the need for precise alignment ofthe optical axis of the converging lenses 21 and 21' shown in FIG. 7. Inthe case of the reflection system of FIG. 7, the object is to detectprotruding parts and like elevations on the surface of the glass sheet.The system of FIG. 7 is more complicated than the basic system of FIG. 4since in the former case two separate optical systems must be providedfor inspecting both surfaces of the sheet glass. Since the apparatus ofthe reflection system of FIG. 7 detects only surface irregularities, itis more advantageous for the detection and prevention of cracks offissures produced during manufacture.

Generally, the longitudinal side edges of the glass sheet drawn from themelting furnace have irregular shapes. Therefore, it may be critical insome applications to project the laser beams obliquely to the surface ofthe glass sheet in a preferred or acute angle as in the aboveembodiment. The laser beams, thus entering the surface of the glasssheet and not entering the side edges of the sheet, assure the correctdetection of defects; and irregular forms or shapes of the side edges ofthe glasssheet will not adversely affect the detection results. Theangle of incidence can be controlled by changing the location of thelight projecting means. By changing the swing angle of the laser beamsor the width of scanning, defects can be detected in a desired isolatedportion of the surface of the glass sheet.

When using the above described polyhedral rotary mirror, the width ofthe laser beams may be increased or decreased by changing the number ofmirrors, and the speed of rotation of the mirror may also be changed toalter the scan period. If an oscillating or vibrating mirror is used, asin the embodiment shown in FIG. 7,

the angle through which the mirror is turned or the frequency ofoscillation of the mirror may be varied so as to adjust the accuracy ofdetection.

Further modifications can be made in the arrangements described withoutdeparting from the scope of the invention.

I claim:

1. Apparatus for detecting irregularities contained in glass sheet,comprising laser beam projecting means mounted adjacent to andsubstantially aligned with one longitudinal edge of said glass sheet fordirecting a laser beam transversely across a longitudinally movingelongated sheet of glass from a point beyond one longitudinal edge ofsaid sheet in the direction of the width of said sheet, means forperiodically oscillating said beam about said point in an acute arc toscan the whole width of said sheet, said beam intersecting said sheet atan acute angle over the whole width of said sheet as it moves from oneedge of the sheet to the other, receiving means fixedly positionedalongside the opposite longitudinal edge of said sheet for receiving aportion of said beam from said sheet during said scanning to generate asignal corresponding to the intensity of said beam and detection circuitmeans connected to receive said receiving means output signal fordetecting varia tions in the amplitude thereof with respect to apredetermined level during each said scan and for issuing a defectsignal indicative of said variations.

2. The apparatus of claim 1, wherein the point from which said beam isdirected across such sheet is spaced from the plane of said sheet suchthat said beam is projected during scanning in a direction nearlyparallel to the width of said sheet.

3. The apparatus of claim 2, wherein said beam intersects said sheet atapproximately the same acute angle over the whole width of said sheet.

4. The detecting apparatus according to claim 1, wherein said laser beamprojecting means includes a laser oscillator for generating a laser beamand at least one oscillating mirror operatively aligned with said laseroscillator for deflecting said laser toward said sheet.

5. The detecting apparatus according to claim 1, wherein said laser beamprojecting means includes a laser oscillator for generating a laser beamand a polyhedral rotary mirror mounted for rotation to deflect saidlaser beam toward said sheet.

6. The detecting apparatus according to claim 1, wherein said laserprojecting means is spaced obliquely from said one edge of said sheetsuch that during said scanning said beam is incident on said sheet at anacute angle to the surface thereof.

7. The detecting apparatus according to claim 1, wherein said light beamreceiving means includes a fiber optic element and a photoelectricconverter for receiving the light fromsaid beam conducted by said fiberoptic element.

8. The apparatus of claim 7, wherein said fiber-optic element has areceiving end which is disposed adjacent to said opposite edge tosubtendthe arc swept out by said beam during scanning of said sheet.

9. The apparatus of claim 8, wherein the length of said receiving end issubstantially less than the width of said sheet.

10. The detecting apparatus according to claim 1,6

wherein said detection circuit means includes a discriminator circuitoperatively receiving the output of said light receiving means forcomparison thereof with a predetermined signal level, said discriminatorcircuit generating an output pulse when said predetermined signal levelexceeds said light receiving means output during each said scan,rand anoutput circuit connected to be energized by said discriminator circuitoutput pulse for generating a defect signal for a predetermined periodof time.

11. Apparatus for detecting defects and irregularities contained inglass sheet drawn from a melting furnace and transferred via at leastone pair of opposing takeup rolls, comprising laser beam projectingmeans mounted adjacent to one longitudinal edge of said glass sheetbetween said melting furnace and a first pair of said take-up rolls forprojecting a laser beam into the surface of said sheet during transferthereof and repeatedly scanning said beam across the surface of saidsheet, laser beam receiving means operatively mounted adjacent the otherlongitudinal edge of said sheet between said melting furnace and saidfirst pair of take-up rolls to receive a portion of the light in saidbeam from said sheet surface during said scanning for generating asignal corresponding to the intensity of the light thus received, and adetection circuit operatively connected to said receiving means fordetecting variations of the amplitude of said receiving means outputsignal and for issuing a defect signal indicative of said variations.

12. The apparatus of claim 11, wherein said beam projecting meansincludes means for directing said beam transversely across said sheetfrom a point beyond said one edge in the direction of the width of saidsheet and spaced from the plane of said sheet such that said beam isprojected during scanning in a direction nearly parallel to the width ofsaid sheet.

13. The apparatus of claim 11, wherein said receiving means isstationary.

14. The apparatus of claim 1 1, wherein said receiving means includes afiber-optic element having a receiving end fixedly positioned to subtendthe arc swept out by said beam during scanning and a photoelectricconverter for receiving the light from said beam conducted by saidfiber-optic element. I

15. The apparatus of claim 14, wherein the length of said receiving endof said fiber-optic element is substantially less than the width of saidsheet.

16. A method of automatically detecting defects and irregularitiescontained in glass sheet, comprising the steps of directing a laser beamtransversely across a longitudinally moving elongated sheet of glassfrom a point substantially aligned with and beyond one longitudinal edgeof said sheet in the direction of the width of said sheet, periodicallyoscillating said beam about said point in an acute arc to scan the wholewidth of said sheet, said beam intersecting said sheet at an acute angleover the whole width of said sheet as it moves from one edge of thesheet to the other, receiving at a stationary location along theopposite edge of said sheet a portion of said laser beam from said sheetduring said scanning, and continuously detecting the presence andabsence of irregularities in said sheet from variations of intensity ofthe received beam.

17. The method of claim 16, wherein said beam is projected across saidsheet in a direction nearly parallel to the width of said sheet.

- l8. Themethod of claim 17, wherein said beam intersects said sheet atapproximately the same acute angle over the whole width of said sheet.

21. The method of claim 16, further comprising the step of detecting thetime within each scanning period at which said variations occur.

22. The method of claim 16,wherein said point is spaced from the planeof said sheetsuch that said beam is projected in a direction nearlyparallel to the width of said sheet during scanning.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. v3,737,665 Dated June 5 1973 Inventor(s) Yasuyuki Naqae It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 23, "presecne" should read -presence.

Column 2, line 9 "of sheet without" should read L-of sheet glass iiwhont Column 3, line 60 "electrical" should read --electric-'. Column 4,line 17, "gate is in the" should read -gate is the-. Column 4, line 61,"thorugh" should read through.

The'formu-la appearing after line 21 in Column 5, "n'N ,thus .b a,"

should read n'N'b a,. Column 5, line 26, "a" should be italicized.

Signed and sealed this 12th day of February 1974.

(.SEAL) Attest:

EDWARD M.FLIETCHER,JR. I c. MARSHALL DANN Commissioner of PatentsAttesting Officer

1. Apparatus for detecting irregularities contained in glass sheet,comprising laser beam projecting means mounted adjacent to andsubstantially aligned with one longitudinal edge of said glass sheet fordirecting a laser beam transversely across a longitudinally movingelongated sheet of glass from a point beyond one longitudinal edge ofsaid sheet in the direction of the width of said sheet, means forperiodically oscillating said beam about said point in an acute arc toscan the whole width of said sheet, said beam intersecting said sheet atan acute angle over the whole width of said sheet as it moves from oneedge of the sheet to the other, receiving means fixedly positionedalongside the opposite longitudinal edge of said sheet for receiving aportion of said beam from said sheet during said scanning to generate asignal corresponding to the intensity of said beam and detection circuitmeans connected to receive said receiving means output signal fordetecting variations in the amplitude thereof with respect to apredetermined level during each said scan and for issuing a defectsignal indicative of said variations.
 2. The apparatus of claim 1,wherein the point from which said beam is directed across such sheet isspaced from the plane of said sheet such that said beam is projectedduring scanning in a direction nearly parallel to the width of saidsheet.
 3. The apparatus of claim 2, wherein said beam intersects saidsheet at approximately the same acute angle over the whole width of saidsheet.
 4. The detecting apparatus according to claim 1, wherein saidlaser beam projecting means includes a laser oscillator for generating alaser beam and at least one oscillating mirror operatively aligned withsaid laser oscillator for deflecting said laser toward said sheet. 5.The detecting apparatus according to claim 1, wHerein said laser beamprojecting means includes a laser oscillator for generating a laser beamand a polyhedral rotary mirror mounted for rotation to deflect saidlaser beam toward said sheet.
 6. The detecting apparatus according toclaim 1, wherein said laser projecting means is spaced obliquely fromsaid one edge of said sheet such that during said scanning said beam isincident on said sheet at an acute angle to the surface thereof.
 7. Thedetecting apparatus according to claim 1, wherein said light beamreceiving means includes a fiber optic element and a photoelectricconverter for receiving the light from said beam conducted by said fiberoptic element.
 8. The apparatus of claim 7, wherein said fiber-opticelement has a receiving end which is disposed adjacent to said oppositeedge to subtend the arc swept out by said beam during scanning of saidsheet.
 9. The apparatus of claim 8, wherein the length of said receivingend is substantially less than the width of said sheet.
 10. Thedetecting apparatus according to claim 1, wherein said detection circuitmeans includes a discriminator circuit operatively receiving the outputof said light receiving means for comparison thereof with apredetermined signal level, said discriminator circuit generating anoutput pulse when said predetermined signal level exceeds said lightreceiving means output during each said scan, and an output circuitconnected to be energized by said discriminator circuit output pulse forgenerating a defect signal for a predetermined period of time. 11.Apparatus for detecting defects and irregularities contained in glasssheet drawn from a melting furnace and transferred via at least one pairof opposing take-up rolls, comprising laser beam projecting meansmounted adjacent to one longitudinal edge of said glass sheet betweensaid melting furnace and a first pair of said take-up rolls forprojecting a laser beam into the surface of said sheet during transferthereof and repeatedly scanning said beam across the surface of saidsheet, laser beam receiving means operatively mounted adjacent the otherlongitudinal edge of said sheet between said melting furnace and saidfirst pair of take-up rolls to receive a portion of the light in saidbeam from said sheet surface during said scanning for generating asignal corresponding to the intensity of the light thus received, and adetection circuit operatively connected to said receiving means fordetecting variations of the amplitude of said receiving means outputsignal and for issuing a defect signal indicative of said variations.12. The apparatus of claim 11, wherein said beam projecting meansincludes means for directing said beam transversely across said sheetfrom a point beyond said one edge in the direction of the width of saidsheet and spaced from the plane of said sheet such that said beam isprojected during scanning in a direction nearly parallel to the width ofsaid sheet.
 13. The apparatus of claim 11, wherein said receiving meansis stationary.
 14. The apparatus of claim 11, wherein said receivingmeans includes a fiber-optic element having a receiving end fixedlypositioned to subtend the arc swept out by said beam during scanning anda photoelectric converter for receiving the light from said beamconducted by said fiber-optic element.
 15. The apparatus of claim 14,wherein the length of said receiving end of said fiber-optic element issubstantially less than the width of said sheet.
 16. A method ofautomatically detecting defects and irregularities contained in glasssheet, comprising the steps of directing a laser beam transverselyacross a longitudinally moving elongated sheet of glass from a pointsubstantially aligned with and beyond one longitudinal edge of saidsheet in the direction of the width of said sheet, periodicallyoscillating said beam about said point in an acute arc to scan the wholewidth of said sheet, said beam intersecting said sheet at an acute angleover the whole width of said shEet as it moves from one edge of thesheet to the other, receiving at a stationary location along theopposite edge of said sheet a portion of said laser beam from said sheetduring said scanning, and continuously detecting the presence andabsence of irregularities in said sheet from variations of intensity ofthe received beam.
 17. The method of claim 16, wherein said beam isprojected across said sheet in a direction nearly parallel to the widthof said sheet.
 18. The method of claim 17, wherein said beam intersectssaid sheet at approximately the same acute angle over the whole width ofsaid sheet.
 19. The method of claim 16, wherein the step of receiving aportion of said beam from said sheet includes receiving the portion ofsaid beam transmitted through said sheet during scanning.
 20. The methodof claim 16, wherein the step of receiving the portion of said beam fromsaid sheet includes receiving the portion of said beam reflected fromthe surface of said sheet during said scanning.
 21. The method of claim16, further comprising the step of detecting the time within eachscanning period at which said variations occur.
 22. The method of claim16, wherein said point is spaced from the plane of said sheet such thatsaid beam is projected in a direction nearly parallel to the width ofsaid sheet during scanning.